Method of controlling supercharger to avoid pulsation



P. S. HOPPER Dec. 7, 1954 METHOD OF CONTROLLING SUPERCHARGER TO AVOIDPULSATION Filed Oct. 14, 1949 SOURCE POWER I WORM DH/ VE MPL/F/ER luoyuew' ATTORNEY Pad ALL Jun arms 31 33g; TEMPE/mum:-

70 ENE/ME United States Patent METHOD OF CONTROLLING SUPERCHARGER TOAVOID PULSATION Philip S. Hopper, Manchester, Conn., assignor to UnitedAircraft Corporation, East Hartford, Conn., a corporation of DelawareApplication October 14, 1949, Serial No. 121,342 8 Claims. (Cl. 230115)curve in the surging range is not the same for all compressors and canbe different in different installations. Operation within this range isundesirable because of the detrimental effects on compressor loading andon compressor efficiency. Various effects of surging which have beennoted in tests include a definite increase in inlet-air temperature, ahigh degree of turbulence and definite prerotation at the compressorinlet annulus, and a large radial temperature gradient at the compressorinlet. 7

The remedy for surging is to alter the operating characteristics of thecompressor. This can be done by varying the angle of attack of vanesmounted adjacent the compressor impeller inlet, or by the use of a bleedin the delivery conduit of the compressor through which a portion of thedischarge flow is dissipated, or recirculated to the compressor inlet.

Surging is a cycle of events in which there is a recirculation of airthrough the compressor. The mixing of the heated air flowing backthrough the compressor with the cooler inlet air results in atemperature gradient in the air stream adjacent to the impeller, beingparticularly large at the compressor inlet annulus. It has been ob-,served that any major surging is preceded by an initial recirculation,and by observing the temperature gradient at some point in the airstream adjacent to the compressor impeller it is possible to anticipatedetrimental conditions of operation in time to alter the compressoroperating characteristics and avoid these'conditions.

An object of this invention is to extend the operating range of acompressor.

. Another object of this invention is to provide a control which willassure surge-free operation of a compressor.

A further object of this invention is to provide a control which isresponsive to changes in the radial temperature gradient existing in theair stream adjacent to a compressor impeller and will preventdetrimental operation of the compressor.

Although the novel features which are characteristics of this inventionare set forth more in detail in the claims appended hereto, the natureand scope of the invention may be better understood by referring to thefollowing description, taken in connection with the accompanying drawingforming a part thereof, in which a specific embodiment has been setforth for purposes of illustration.

In the drawing:

Fig. 1 is a vertical section through a centrifugal compressor utilizingthe control apparatus.

Fig. 2 is a fragmentary view of an alternate arrangement of the controlapparatus.

Fig. 3 is a vertical section through an axial flow compressor showingthe thermocouples mounted on the inlet side of the first compressorstage.

Fig. 4 is .a modification of Fig. 3, showing the thermo-v 2,696,345Patented Dec. 7, 1954 "ice couples mounted on the delivery side of thefirst compressor stage.

Referring to Fig. 1 in detail, the compressor includes bladed impeller10 mounted on drive shaft 12, inlet casing 14, and outlet casing 20.Casing 14 defines inlet conduit 16 and inlet annulus 18 and surroundsimpeller 10 to define therewith a continuation of the inlet conduit.Casing 20 defines delivery conduit 22 and is connected to an aircraftengine, not shown. The outer casing includes diffuser vanes 24 mountedwithin the delivery conduit adjacent to the delivery side of theimpeller, and port 26 for bleeding air from the delivery conduit.

A pair of thermocouples 28 and 30 are mounted within the inlet annulus18. These thermocouples are located adjacent to and at approximately anequal distance from the impeller inlet face, and radially spaced apartso as to be responsive to a radial temperature gradient across theimpeller inlet. The thermocouples are balanced, being wired in seriesand having opposed polarity, and their leads 32 are connected to acommon junction box 34 in order that the three junctions 36, 38 and 40can be maintained at the same temperature. Junction 38 is common to thetwo thermocouples and junctions 36 and 40 are connected by leads 42 and44, respectively, to servo amplifier 46 which in turn is connected to apower source, not shown.

Servo amplifier 46 is connected by leads 48 to reversing motor 50 whichoperates worm drive 52 to regulate the position of bleed valve 54 withinport 26, the valve 22mg drivingly connected to the worm drive by shaftAn alternative arrangement is shown in Fig. 2 in which the reversingmotor 50 and worm drive 52 of Fig. 1 function to vary the angle ofattack of vane 58 located within the inlet annulus 18. This vane isdrivingly connected to the worm drive by shaft 60. While only one vaneis. shown for simplicity, it is to be understood that, as is common inthe art, a series of such vanes would be provided around the inletannulus.

When recirculation occurs within the vicinity of the impeller inletindicating the onset of surge, the temperature of thermocouple 28mounted adjacent the outer wall of the inlet annulus, will increase withrespect to that of thermocouple 30, mounted adjacent the inner wall ofthe inlet annulus, creating a potential difference between thethermocouples and causing a signal to be relayed to servo amplifier 46.The servo amplifier in turn will respond to this signal by operatingreversing motor 50 so as either to open bleed valve 54 or change theangle of attack of vanes 58, Whichever system is used. In either casethe result is to alter. the operating characteristics of the compressor,thus anticipating surge and avoiding its detrimental effects. Whenstable operating conditions have been established, and the radialtemperature gradient at the impeller has become normal, the servoamplifier will function in response to'this signal to restore either thebleed valve or the vanes to their original position.

Fig. 3 illustrates the use of the control apparatus in connection withan axial flow compressor, 62 indicating a bladed impeller mounted ondrive shaft 66. The inlet annulus is defined by inner casing 68 andouter casing 70, the outer casing carrying stationary vanes 71. pair ofbalanced thermocouples 72 and 74 are mounted in a radial plane withinthe inlet annulus adjacent to the impeller and are connected to junctionbox 76. These thermocouples function in the same manner as thosedescribed in connection with Fig. 1 to operate a bleed on'the deliveryside of the impeller or to vary the angle of attack of vanes mountedwithin the inlet annulus. Fig. 3 shows neither a bleed nor vanes, but itis understood that either arrangement could be used as taught in Fig. land Fig. 2.

Rather than using temperature responsive elements mounted adjacent theimpeller inlet, it would be possible to place these elements on thedelivery side of the impeller. In Fig. 4, balanced thermocouples 78 and80 are shown mounted downstream of impeller 62, as on the stationaryvanes 71. These thermocouples are connected to junction box 82 and canbe arranged to vary the operating characteristics of the compressor inresponse to a potential difference therebetween.

It is to be understood that the invention is not limited to the specificembodiments herein illustrated and described, but may be used in otherways without departure from its spirit as defined by the followingclaims.

I claim:

1 A compressor including a rotatable impeller having an inlet side and adelivery side and casing means having inner and outer walls defining anannular conduit for the flow of air through said compressor, said wallsextending upstream and downstream of said impeller, in combination witha surge control comprising essentially a plurality of temperaturesensing elements mounted in said conduit adjacent to one of saidimpeller sides, said elements being spaced apart transversely of theconduit, substantially equally spaced from the impeller longitudinallyof the conduit, with at least one of said elements being locatedadjacent said inner Wall and at least one of said elements being locatedadjacent said outer wall of said casing, means cooperating with saidconduit to aflect the flow of air therethrough thereby altering theoperating characteristics of said compressor, and anoperative connectionbetween said temperature sensing elements and said operatingcharacteristic altering. means including means responsive to atemperature difference between said elements for actuating saidoperating characteristic altering means.

2. A compressor including a rotatable impeller having an inlet side anda delivery side and easing means having inner and outer walls definingan annular conduit for the flow of air through said compressor, saidwalls extending upstream and downstream of said impeller, in combinationwith a surge control comprising essentially a pair of temperaturesensing elements mounted in said conduit adjacent to one of saidimpeller sides, said elements being spaced apart transversely of theconduit, substantially equally spaced from the impeller longitudinallyof the conduit, with one of said elements being located adjacent saidinner wall and the other of said elements being located adjacent saidouter wall of said casing, means cooperating with said conduit to affectthe flow of air therethrough thereby altering the operatingcharacteristics of said compressor, and an operative connection betweensaid temperature sensing elements and said operating characteristicaltering means including means responsive to a temperature differencebetween said elements for actuating said operating characteristicaltering means.

3. A compressor including a rotatable impeller having an inlet side anda delivery side and casing means having inner and outer walls definingan annular conduit for the flow of air through said compressor, saidwalls extending upstream and downstream of said impeller, in combinationwith a surge control comprising essentially a pair of balancedthermocouples mounted in said conduit adjacent to one of said impellersides, said thermocouples being substantially equally spaced from theimpeller longitudinally of the conduit with one of said thermocouplesbeing located adjacent said inner wall and the other of saidthermocouples being located adjacent said outer wall of said casing,means cooperating with said conduit to affect the flow of airtherethrough thereby altering the operating characteristics of saidcompressor, and an operative connection between said thermocouples andsaid operating characteristic altering means including means responsiveto a potential difference between the thermocouples for actuating saidoperating characteristic altering means.

4. A compressor including a rotatable impeller having an inlet side anda delivery side and easing means having inner and outer walls definingan annular conduit for the flow of air through said compressor, saidwalls extending upstream and downstream of said impeller, in combinationwith a surge control comprising essentially a pair of thermocoupleswired in series and of opposed polarity mounted in said conduit adjacentto one of said impeller sides, said thermocouples being substantiallyequally spaced from the impeller longitudinally of the conduit with oneof said thermocouples being located adjacent said inner wall and theother of said thermocouples being located adjacent said outer wall ofsaid casing, a servo amplifier operatively connected to thethermocouples and responsive to a potential difference therebetween,means cooperating with said conduit to affect the flow of airtherethrough thereby altering the operating' characteristics'of' saidcompressor, and a reversing motor operatively connected to the servoamplifier and to said operating characteristic altering means, saidamplifier actuating said reversing motor whenever a radial temperaturegradient across said conduit creates a potential difference between saidthermocouples.

5. A compressor including a rotatable impeller having an inlet side anda delivery side and casing means having inner and outer walls definingan annular conduit for the flow of air through said compressor, saidwalls extending upstream and downstream of said impeller, in combinationwith a surge control comprising essentially a pair of thermocoupleswired in series and of opposed polarity mounted in said conduit adjacentto the inlet side of said impeller, said thermocouples beingsubstantially equally spaced from the impeller longitudinally of theconduit with one of said thermocouples being located adjacent said innerwall and the other of said thermocouples being located adjacent saidouter Wall of said casing, means cooperating with said conduit to affectthe flow of air therethrough thereby altering the operatingcharacteristics of said compressor, and an operative connection betweensaid'thermocoupl'es and said operating characteristic altering meansincluding means responsiveto a temperature difference between saidthermocouples for actuating said operating characteristic alteringmeans.

6. A compressor including a rotatable impeller having an inlet side anda delivery side and easing means having inner and outer walls definingan annular conduit for the flow of air through said compressor, saidwalls extending upstream and downstream of said impeller, in combinationwith a surge control comprising essentially a pair of thermocoupleswired in series and of opposed polarity mounted in said" conduit ad'-jacent to the delivery side of said impeller, said thermocouples beingsubstantially equally spaced from the impeller longitudinally of theconduit with one of said thermocouples being located adjacent said.inner wall and the other of said thermocouples being located adjacentsaid outer wall of said casing, means cooperating with said conduit toaffect the flow of air therethrough thereby altering the operatingcharacteristics of said compressor, and an operative connection betweensaid thermocouples and said operating characteristic altering meansincluding means responsive to a temperature difference between saidthermocouples for actuating said operating characteristic alteringmeans.

7. A compressor including a rotatable impeller having an inlet side anda delivery side, casing means having inner and outer walls defining anannular conduit for the flow of air through said compressor, said wallsextending upstream and downstream of said impeller, at least one bleedport located in said casing means ad'- jacent to the delivery side ofsaid impeller and valve means controlling the area of said bleed port,in combination with a surge control comprising essentially a pair ofthermocouples mounted in said conduit adjacent to one of said impellersides, said thermocouples being substantially equally spaced from theimpeller longitudinally of the conduit with one of said thermocouplesbeing located adjacent said inner wall and the other of saidthermocouples being located adjacent said outer wall of said casing, andan operative connection between said thermocouples and said bleed portvalve means including means responsive to a temperature differencebetween said thermocouples for actuating said valve means.

8. A compressor including a rotatable impeller having an inlet side anda delivery side, casing means having inner and outer walls defining anannular conduit for the flow of air through said compressor, said wallsextending upstream and downstream of said impeller, a plurality of guidevanes mounted within said casing means adjacent to the inlet side ofsaid impeller and means controlling the angle of attack of said guidevanes, in combination with a surge control comprising essentiallya pairof thermocouples mounted in said conduit adjacent to one of saidimpeller sides, said thermocouples being substantially equally spaeedfrom the impeller longitudinally of the conduit with one of saidthermocouples being located adjacent'said innerwall and the other ofsaid thermocouples being located adjacent said tauter wall 03 saidcasing, and andoperiative (fonnec- References Cited in the file of thispatent tion etween sai t ermocoup es an sai gui e vane angle of attackcontrolling means including means re- UNITED STATES PATENTS sponsive toa temperature difference between said therrno- Number Name Date couplesfor actuating said angle of attack controlling 5 1,281,216 SchellensOct. 8, 1918 means. 2,000,721 Standerwick May 7, 1935 2,442,049 Lee May25, 1948 2,455,292 Borden Nov. 30, 1948

